Lithographic printing plate containing a di(tetrahydrofurfuryl) ester

ABSTRACT

DI(TETRAHYDROFURFURYL) ESTERS HAVING NO MORE THAN 20 CARBON ATOMS PARTICULARLY THOSE HAVING THE FOLLOWING GENERAL FORMULA: IN WHICH R IS A DIVALENT ORGANIC ACID RADICAL, USED EITHER ALONE OR FOR INCORPORATING DEVELOPING AGENTS IN PHOTOGRAPHIC ELEMENTS TO INCREASE THE LITHOGRAPHIC LATITUDE IN LITHOGRAPHIC PLATS EMPLOYING A GELATIN IMAGE AREA AND A GELATIN NON-IMAGE AREA.   2-((TETRAHYDROFUR-2-YL)-CH2-O-R-O-CH2-)TETRAHYDROFURAN

Aprll 27, 1971 R WOODWARD ETAL 3,576,634

LITHOGRAPHIC PRINTING PLATE CONTAINING A DI(TETRAHYDROFURFURYL) ESTER Filed May 1, 1968 EXPOSURE EMULSION CONTA/IVl/VG DEVELOP/N6 AGE/VT SUPPORT EXPOSURE 2 ALKALINE ACTIVATION, M/Kl/VG EMULSION (FOGGEO/ CONTA/N/NG Q DEVELOP/N6 AGENT SUPPORT Rosmr 1v. wooowmo JOE E. SOUTH INVENTORS A T TOR/VEY United States Patent US. Cl. 96-95 28 Claims ABSTRACT OF THE I DISCLOSURE Di(tetrahydrofurfuryl) esters having no more than carbon atoms particularly those having the following general formula:

r r -r H2O CHCHzOROHzCHC CH2 in which R is a divalent organic acid radical, used either alone or for incorporating developing agents in photographic elements to increase the lithographic latitude in lithographic plates employing a gelatin image area and a gelatin non-image area.

This invention relates to photographic emulsions and elements. In one embodiment, this invention relates to emulsions containing liquid di(tertrahydrofurfuryl) esters as solvents for incorporated silver halide developing agents.

It is advantageous for some purposes to incorporate developing agents in silver halide emulsions. Developing agents which are Water insoluble can be incorporated into such emulsions using certain oil solvents such as, for instance, tricresyl phosphate, dibutyl phosphate, etc. It appears that the solvent containing the developer is in liquid particles in the dried emulsion.

In certain photographic elements, the dispersed developing agents are incorporated in a layer adjacent to the silver halide emulsion layer. A particularly useful silver halide sensitized lithographic printing plate is described in U.S. Pat. 3,146,104 issued Aug. 25, 1964, to Yackel and Abbott. In one embodiment of this lithographic plate, the support contains a gelatin layer having therein an incorporated developing agent over which is coated a light sensitive silver halide emulsion followed by a top layer of a fogged silver halide emulsion. Following exposure and activation, the developing agent develops the light sensitive emulsion in the exposed areas while the developing agent in the unexposed areas migrates to the top fogged emulsion where development takes place to obtain a direct positive image. Successful operation of the resulting lithographic plate depends upon the ink-Water diiferential between the image areas and non-image areas in the top colloid layer. Migration of an oil solvent to this layer can reduce the hydrophilic nature of the non-image areas and can decrease the ink-water diiferential. There fore, it has been desirable to find a solvent for the developer Which would improve the ink-water dilferential.

In another embodiment the 3-layer system of the prior art product is replaced with a single layer which provides a direct positive in which a direct positive emulsion contains incorporated silver halide developing agents. It has been desirable to find a developer solvent which would increase the ink-water difierential in this embodiment and which would provide other desirable characteristics such as good solvent action for the developer, etc.

We have now found a method of improving the lithographic difierential by incorporating di(tetrahydrofurfuryl) esters in photographic elements and also a method of incorporating developers in emulsions, or in a layer integral with the emulsion wherein liquid di(tetrahydrofurfuryl) esters are used instead of other oil solvents or in place of part of the oil solvents conventionally used.

One object of this invention is to provide a process of using di(tetrahydrofurfuryl) esters in lithographic elements. Another object is to provide a method of using di (tetrahydrofurfuryl) esters as liquid solvents for silver halide developing agents dispersed in silver halide emulsions or in layers adjacent to or integral with the emulsion. Another object is to provide a photographic element having at least one incorporated developing agent in a di (tetrahydrofurfuryl) ester in the silver halide emulsion. A further object is to provide lithographic printing plates having thereon direct positive silver halide emulsions con taining incorporated developing agents. A still further object is to provide a lithographic element having improved lithographic difierential, better physical properties and better emulsion stability containing in at least one layer a di(tetrahydrofurfuryl) ester. A still further object is to provide a method of making silver halide emulsions having therein an incorporated developing agent. Additional objects will be evident from the following disclosure.

The above objects are obtained by the use, in silver halide emulsions or in colloid layers adjacent to silver halide emulsion layers, of di(tetrahydrofurfuryl) esters which are normally liquid, i.e. liquid at a temperature of about 25 C. A preferred chain of esters of this type can be represented by the general formula:

in which R is a divalent organic acid radical such as for example, phthalyl, succinyl, adipyl, glutaryl, and the like provided the esters have no more than 20 carbon atoms. More specifically, R can be dicarboxylic radicals including radicals substituted with hydroxy, alkyl having 1-4 carbon atoms, amino, carboxy alkyl, sulfo alkyl, etc.

The di(tetrahydrofurfuryl) ester may be used in the photographic element either alone or as a solvent for developing agents in an amount of 50 to 1000 mg./ft. of coating, preferably to 450 mg./ft. When used as a developing agent solvent, the concentration of di(tetrahydrofurfuryl) ester solvent to developing agent is advantageously within the range of about 1:1 to about 1:15 by weight, preferably 1:4 to 1:7. If used in conjunction with an oil solvent such as other liquid inert esters, it can be mixed in any proportion. However, a particularly advantageous solvent mixture comprises at least 25% by weight of the di(tetrahydrofurfuryl) ester solvent. The oil solvents for developing agents are substantially water insoluble, low molecular weight, organic oils having boiling points above about 150 C. and having high solvent action for silver halide developing agents.

One embodiment of our invention relates to a lithographic printing plate comprising a support having thereon a gelatin layer containing di(tetrahydrofurfuryl) succinate in which is dispersed a silver halide developing agent such as, for example, 4-phenyl-catechol. Over this layer is an unfogged photographic silver halide emulsion and a fogged silver halide emulsion. After exposing to a. light image, the plate is processed in an alkaline activator and printed on a lithographic printing press.

Another embodiment of our invention relates to a lithographic printing plate comprising a direct positive emulsion having therein a liquid di(tetrahydrofurfuryl) ester such as, for example, di(tetrahydrofurfuryl) adipate in which is dispersed a silver halide developing agent such as, for example, 4-phenyl catechol. This plate is exposed, processed in an alkaline activator solution and printed on a lithographic printing press giving a positive lithographic print. I

In still another embodiment of our invention, a direct positive emulsion as described above also contains an oil solvent such as, for example, tricresyl phosphate. The lithographic plate is exposed as above and used on a lithographic printing press to give a positive lithographic print.

Silver halide emulsions which are used in the practice of our invention include the conventional silver halide emulsions such as silver chloride, silver bromide, silver iodide, silver chlorobromide, silver bromoiodide and silver chlorobromoiodide.

In the practice of this invention, the ink receptive areas of the printing plates on a background of hydrophilic material are obtained by alkaline activation of a silver salt, preferably silver halide, developing agent in the presence of a gelatin, silver salt emulsion layer. The result is to form a silver image and oxidized developing agent in the region of development. The element can then be inked in the developed areas with greasy printing ink and a positive print made therefrom in a lithographic press. The gelatin in the emulsion layer can undergo additional hardening at the same time as development.

The developing agents employed in the practice of this invention include any developing agents which are capable of oxidation in the presence of the hardened vehicle, e.g. gelatin present in the photographic emulsion layer to produce an image receptive to greasy printing ink, i.e. upon development, they render the vehicle, preferably gelatin in the developed areas oleophilic. The polyhydroxy benzene developing agents substituted with halogen, monocyclic aryl groups of the benzene series and alkyl groups of at least 2 and preferably from 2 to 6 carbon atoms have this property. The 1,2-dihydroxybenzene developing agents substituted by halogen, monocyclic aryl of the benzene series and alkyl groups of at least 2 carbon atoms and preferably 2 to 6 carbon atoms are particularly useful in the process.

Developing agents possessing the necessar properties thus include certain polyhydroxy benzene developing agents such as pyrogallol and substituted polyhydroxy benzene developing agents, particularly dihydroxy benzenes substituted with, for example, halogen, alkyl groups of at least 2 and preferably from 2 to 6 carbon atoms and a monocyclic aryl group of the benzene series, e.g. o-chlorohydroquinone, o-bromohydroquinone, t-butyl hydroquinone, 4-phenyl catechol, 4-t-butyl catechol, pyrogallol, 4-n-butypyrogallol, nordihydroguaiaretic acid, 4,5-dibromo catechol, 3,3,6-tribromo-4-phenyl catechol and l-phenyl- 3-(N-n-hexylcarboxamide) 4- [p- (,B-hydroquinolylethyl) phenylazo]-5-pyrazolone. Esters of such developing agents, e.g. formates and acetates of pyrogallol hydrolyze in alkaline solutions and can be used in the process of the invention. Such esters are intended to be included in the specification and claims where reference is made to polyhydroxy benzene developing agents.

In certain cases, it has been found to be advantageous to include with the polyhydroxy benzene developing agent such as pyrogallol, an auxiliary developing agent such as monomethyl-p-aminophenol or a 3-pyrazolidone which latter developing agents by themselves do not yield oleophilic images in the processes described, but which do appear to act synergistically with the polyhydroxy benzenes to yield oleophilic images. The developing agents are generally employed in the photographic elements at coverages of about 5 to about 200, preferably about to about 50 mg./ft. of support and are incorporated in a layer which is no farther from the support than the photographic emulsion layer, i.e. they are incorporated into the photographic emulsion layer or a layer between the emulsion layer and the support, e.g. an adjacent or contiguous layer.

It will be appreciated that the printing layer in a printing plate of the type disclosed in US. Pat. 3,146,104, should be substantially hardened in order to prevent the process plate from adhering to printing blankets, papers, etc. For this purpose, the emulsion of the printing layer should be as hard as a gelatin layer containing at least about 2 grams and preferably about 2 to 15 grams of dry formaldehyde per pound of gelatin, i.e. it should have a melting point in water greater than 150 F. and preferably greater than 200 F.

Various colloids can be used either with gelatin or substituted for at least a part of the gelatin vehicle or binding agent in the photographic emulsion layers employed in the practice of this invention. However, gelatin or gelatin derivatives which are primarily gelatin, are used for at least a part, for example, at least 10%, by weight, of the binder in the photographic element. Other binding agents which can be used include colloidal materials such as colloidal albumin, cellulose derivatives, synthetic resins, such as polyvinyl compounds, acrylamide polymers, or the like. It is often advantageous to employ combinations of binding agents, particularly mixtures of gelatin with aqueous dispersions of polymerized ethylenically unsaturated compounds. The binding agent is generally coated at a coverage in the range of about 50 to 2000, advantageously about mg. to about 1000 mg. per square foot of support.

Direct positive emulsions which may be used include (1) solarizing silver halide emulsions and (2) internal latent image silver halide emulsions forming the latent image mostly inside the silver halide grains.

The solarizing direct positive silver halide emulsions are silver halide emulsions which have been effectively fogged either chemically or by radiation, to a point which corresponds approximately to the maximum density of the reversal curve as shown by Mees, The Theory of the Photographic Process, published by Macmillan Co., New York, N.Y., 1942, pp. 261297.

Typical methods for the preparation of solarizing emulsions are shown by Groves British Pat. 443,245, Feb. 25, 1936, who subjected an emulsion to Roentgen rays until the emulsion layer, when developed without additional exposure, is blackened up to the apex of its gradation curve; Szaz British Pat. 462,730, Mar. 15, 1937, the use of either light or chemicals such as silver nitrate, organic sulfur compounds and dyes to convert ordinary silver halide emulsions to solarizing direct positive emulsions; Arens US. Pat. 3,005,837, June 25, 1935, the use of silver nitrate and other compounds in conjunction with heat to efiect solarization of the silver halide, and Leermakers US. Pat. 2,184,013, the use of large concentrations of non-acid optical sensitizing dyes and reducing agents to effect solarization.

Kendall and Hill US. Pat. 2,541,472, Feb. 13, 1951, shows useful solarizing emulsions particularly susceptible to an exposure with long wavelength light to produce a Herschel effect described by Mees above, produced by adding nitro substituted electron acceptors and other compounds to the emulsion which is fogged either chemically or with white light. In using the emulsions, a suflicient reversal image exposure is employed using minus blue light of from about 500-700 millimicrons wavelengths, preferably 520-540 millimicrons, to substantially destroy the latent image in the silver halide grains in the region of the image exposure. In these procedures, of course, only non-hardening chemicals are selected for use in fogging the solarizing emulsions if an emulsion is used requiring a given hardness.

Conventional silver halide developing solutions can be used to develop a direct positive image in the solarizing emulsions.

The internal latent image direct positive silver halide emulsions used in the invention are those well known in the art which upon exposure form the latent image mostly inside the silver halide grains, the direct positive properties of the emulsions being attributable to the crystalline structure of the silver halide grains. That is, a number of authorities in the field of photography have shown that'there are imperfections or flaws, in the crystal structure (on the surface or internally) of silver halide which is used in photography, at which flaws the latent image forms by trapping photoelectrons to give development centers. Development therefore, commences at the sites of these flaws. Journal of Photographic Science. Photo graphic Sensitivity, text of a lecture given on July 1, 1957, by J. W. Mitchell; vol. 6, No. 3 (1958).

Other photographic reversal emulsions may be used including those containing grains comprising a central core of a water insoluble silver salt containing centers which promote the deposition of photolytic silver and an outer shell or covering for such core of a fogged or spontaneously developable water insoluble silver salt. The fogged shell of such grains is developed to silver without exposure. Emulsions of this type are described in Berriman U.S. Pat. 3,367,778, issued Feb. 6, 1968.

Before the shell of water insoluble silver salt is added to the silver salt core, the core forming emulsion is first chemically or physically treated by methods previously described in the prior art to produce centers which promote the deposition of photolytic silver, i.e., latent image nucleating centers. Such centers can be obtained by various techniques as described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, vol. XXVIII, January 1957, pages 57-65, are particularly useful. Such chemical sensitization, includes three major classes, namely, gold or noble metal sensitization, sulfur sensitization, such as labile sulfur compound and reduction sensitization, i.e. treatment of the silver halide with a strong reducing agent which introduces small specks of metallic silver into the silver salt crystal or grain.

The core forming emulsions can be chemically sensitized by any method suitable for this purpose. For example, the core forming emulsions can be digested with naturally active gelatin or sulfur compounds can be added to those described in Shepard U.S. Pat. 1,574,944, issued Mar. 2, 1926, Shepard et al. U.S. Pat. 1,623,499, issued Apr. 5, 1927, Shepard et al. U.S. Pat. 2,410,689, issued Nov. 5, 1946.

The core forming emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Pat. 2,399,083, issued Apr. 23, 1946 and Damschroder et al. U.S. Pat. 2,642,361, issued June 16, 1953. Suitable compounds are potassium chloroaurite, potas sium aurithiocyanate, potassium chloroaurate, aurictrichloride and 2-aurosulfobenzothiazole methylchloride.

The core forming emulsions can also be chemically sensitized with reducing agent, such as stannous salts (Carroll U.S. Pat. 2,487,850, issued Nov. 15, 1959), polyamines such as diethylenetriamine (Lowe and Jones U.S. Pat. 2,618,598, issued Aug. 15, 1950), polyamines such as spermine (Lowe and Allen U.S. Pat. 2,521,925, issued Sept. 12, 1950) or bis(beta-aminoethyl)sulfide and its water soluble salts (Lowe and Jones U.S. Pat. 2,521,926, issued Sept. 12, 1950).

The shell of the grains comprising the emulsions used in practicing this invention is prepared by precipitating over the core grains a light sensitive water insoluble silver salt that can be fogged and which fog is removable by bleaching. The shell is of sufficient thickness to prevent access of the developer used in processing the emulsions of the invention to the core. The silver salt shell is surface fogged to make it developable to metallic silver with conventional surface image developing compositions. The silver salt of the shell is sufiiciently fogged to produce a density of at least about 0.5 when developed for 6 minutes at 68 F. in Developer A below when the emulsion is coated at a silver coverage of 100 mg. per square foot.

6 DEVELOPER A N-methyl-p-aminophenol sulfate-2.5 grams Ascorbic acid-10.0 grams Potassium metaborate35.0 grams Potassium bromide1.0 gram Water to 1 liter pH of 9.6

Such fogging can be effected by chemically sensitizing to fog with the sensitizing agents described for chemically sensitizing the core forming emulsion, high intensity light and like fogging means well known to those skilled in the art. While the core need not be sensitized to fog, the shell is fogged, for example, reduction fogged with a reducing agent such as stannous chloride. Fogging by means of a reduction sensitizer, a noble metal salt such as gold salt plus a reduction sensitizer, high pH and low pAg silver halide precipitating conditions, and the like can be suitably utilized. The shell portion of the subject grains can also be coated prior to fogging.

Another direct positive silver halide emulsion which can be used is a fogged direct positive silver halide emulsron comprising silver halide grains which have a uniform diameter frequency distribution, i.e. silver halide grains which have substantially uniform diameter. In one embodiment of this type of emulsion, the direct positive photographic emulsion comprises fogged silver halide grains, at by weight of said grains having a diameter which is within about 40% of the mean grain diameter. Preferably, photographic emulsions of this type comprise reduction and gold fogged silver halide grains and a compound which accepts electrons. The use of low concentrations of reduction and gold fogging agents, in preparing such emulsions gives unique fogged silver halide grains which are characterized by a very high photographic speed in conventional photographic processing solutions.

The photographic layers described herein can be superimposed upon a wide variety of supports. Typical supports include those generally employed in printing plates, as exemplified by metals such as aluminum, paper, cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate and related films or resinous materials and other related materials. Supports include paper which may be partially acetylated or coated with an alpha-olefin polymer, particularly a polymer of an alpha-olefin containing 2-10 carbon atoms, as exemplified by the polyethylene, polypropylene, ethylenebutene copolymers and the like give good results.

A support having particularly good dimensional stability can be prepared which consists of 2 /2-mil layers of polyethylene terephthalate film base between which is laminated a glass layer /2-mil thick. This laminated material has the dimensional stability of metal since it does not stretch under normal printing conditions and the flexible properties of film base. It will be appreciated that other polymeric film materials such as polyamides, cellulose esters and the like can be used in place of the polyethylene terephthalate.

The photographic elements or printing plates of this invention can include antihalation layers which are generally coated between the photographic emulsion layer and the support. Suitable layers of this type include gelatin layers containing organic and inorganic dyes or pigments such as Naphthol Red dye, pigments such as colloidal carbon or silver, zinc oxide, titanium dioxide, iron oxide and the like which can be dyed, if desired, with such dyes as the merocyanines and the like, or paper coated with an alpha-olefin polymer employed as the support. It is also convenient to incorporate a dye and/or a pigment into the resin coating on the photographic emulsion side surface of the support which serves as an antihalation layer. In addition, the dyes and/or pigments can be on the same layer with the polyhydroxybenzene developing agent when it is coated in a layer beneath the photographic emulsion layer.

In the accompanying drawing representative sensitive elements of the invention are shown in greatly enlarged cross-sectional view at various stages of the preparation of lithographic printing plates. In FIG. 1 a negativepositive process is illustrated and in FIG. 2 is shown a positive-positive process contemplated by our invention.

In FIG. 1, layer of the element of stage one represents a support such as paper, film base, etc. Layer 11 is a hydrophilic organic colloid layer such as gelatin containing the developing agent and silver halide.

In the process of FIG. 1, after exposure to a subject as shown in area 12, followed by alkaline activation and inking, the element appears substantially as shown in stage two. Area 14 which is composed of silver and the reaction product of the oxidized developing agent and the hydrophilic organic colloid present in the silver halide emulsion layer produced in the development reaction, carries the ink image 15. The undeveloped area 16 of layer 11 remains hydrophilic and repellent of printing ink when moistened with water.

In FIG. 2 is shown a positive-positive system in stage one of which the element includes a support 20 such as a paper or film support, layer 23 comprising a fogged silver halide emulsion layer containing a developing agent. Upon image exposure in region 24, followed by alkaline activation and inking, the element appears substantially as shown in stage two, the silver halide developing agent of layer 23 having developed a positive silver halide image to silver in areas 25 of layer 23-. The ink images 26 are accepted in areas 25 which are composed of silver and the reaction product of the organic hydrophilic colloid present in the silver halide emulsion layer and the oxidized developing agent. The remaining areas 27 are hydrophilic and repel printing ink when the plate is moistened in the lithographic printing press.

Positive working lithographic plates can be made using conventional negative speed photographic silver halide emulsions containing an oxidizing developer solvent dispersion of this invention by the use of a processing cycle comprising the following steps:

(1) Exposure.

(2) Negative development in a developer, such as Kodak D-72 developer, containing at least 10 grams of sodium sulfite per liter followed by a rinse. These developed areas are hydrophilic. The oxidizing development agents are quite insoluble in the pH range and, consequently, are not washed out during this negative development.

(3) The element is then flashed to light of suflicient intensity to fog the remaining silver halide.

,. (4) Final development to obtain the oxidized, ink-reo ceptive, positive image takes place by immersing the element in a sulfite-free, alkaline solution, e.g. 5% sodium carbonate. I

(5) The surface solution is then removed with a squeegee, press fountain solution applied and the prints run on the lithographic press.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 A control element (Sample A) is made up as follows:

LAYER IDEVELOPER DISPERSION PREPARATION Solution (1) Solution (2) 4-phenylcatechol-63O g. tricresyl phosphate solvent--630O g.

8 The 4-phenylcatechol is added to the solvent and heated at 220 F. until dissolved.

Solution (3 dry photographic gelatin4000 g. distilled water-60,000 ml.

The gelatin is dissolved and melted at F. Solutions (1) and (3) are blended and stirred for 5 minutes. Solution (2) is added and stirred for 5 minutes. The mixture is colloid milled three times.

Melt prepartion7.6 kgs. of dry photographic gelatin is dissolved in 56.5 kgs. of distilled water and melted at F. This is cooled to 107 F. and 75.72 kgs. of the above dispersion is added; also 2000 ml. of 5% of the above wetting agent is added and the combination is coated on polyethylene coated paper base. The coating is applied at 7.16 ml. per square foot giving 31.5 mg. of 4-phenylcatechol per square foot.

LAYER II Green sensitized silver chloride emulsion (1 mole)-- 15% saponin solution200 cc.

2% formaldehyde-40 cc.

Water-2460 g.

The coating is applied at 40 C. on Layer I at 15.0 cc.

sq. ft.

LAYER III Gelatin silver chloride emulsion (l mole)--3300 g. Water-2000 cc.

0.25/N NaOH240 cc.

2% formaldehyde46= cc.

Hold for 40 minutes at 40 C. to fog, then add:

2.0/N H SO 35 cc.

15 saponin solution-l00 cc. Water-729 cc.

The coating is applied at 40 C. on Layer II at 45 mg. of Ag/sq. ft. and 182 mg. of gelatin per square foot.

EXAMPLE 2 An element similar to Example 1 is made which diifers only in that Layer I, 315 mg. of di(tetrahydrofurfuryl) adipate per square foot is included therein and the level of tricresyl phosphate is reduced to 189 mg. per square foot.

EXAMPLE 3 An element similar to Example 2 is prepared which differs only in that the gelatin level in Layer III is reduced to 25% of the previous level or 73 mg. per square foot.

The three elements of Examples l-3 are exposed to a line positive, processed 60 seconds in 4 percent trisodium phosphate solution, treated in a 2 percent aqueous acetic acid stop bath for 1 minute, squeegeed to remove excess liquid and run on a lithographic printing press using a. relatively high tack ink.

Additional press runs are made in like manner except that lower tack inks, A and B, are utilized. The press results are summarized below:

A positive working presensitized lithographic printing plate is prepared using a reversal emulsion of the type described in the Berriman U.S. Pat. 3,367,778 referred to above in combination with polyhydroxybenzene develop ing agents located in an adjacent layer beneath the photographic emulsion layer. To the emulsion are added the various oil solvent dispersions of 4-phenylcatechol as described below. The emulsion containing the incorporated developer agent dispersions is then coated, at 440 ft. per silver mole, over a paper support which contains a sublayer of TiO pigmented polyethylene and a backing layer of clear polyethylene.

Sample A.The emulsion contains a dispersion of- 60 grams of 4-phenylcatechol in 300 grams tricresyl phosphate solvent.

Sample B.-The emulsion contains a dispersion of 60 grams of 4-phenylcatechol in 300 grams of dibutyl phthalate solvent.

Sample C.The emulsion contains a dispersion of 60 grams of 4-phenylcatechol in 300 grams di(tetrahydrofurfuryl) succinate solvent.

Sample D.The emulsion contains a dispersion of 60 grams of 4-phenylcatechol in a combination of 240 grams of tricresyl phosphate solvent and 60 grams of di(tetrahydrofurfuryl) succinate solvent.

Sample E.-The emulsion contains a dispersion of 60 grams of 4-phenylcatechol in 180 grams of tricresyl phosphate solvent and 120 grams of di-(tetrahydrofurfuryl) succinate solvent.

Sample F.The emulsion contains a dispersion of 60 grams of 4-phenylcatechol in 120 grams of tricresyl phosphate solvent and 180 grams of di(tetrahydrofurfuryl) succinate solvent.

The direct positive photosensitive elements obtained are exposed by projection to a line original in a conventional process camera. After 20 seconds activation at 75 F. in an 8% potassium phosphate solution, the plates are stopped in a phosphoric acid bath. The plates are then printed on a lithographic press giving a positive lithographic print.

The following results are obtained from the testing of the elements represented by Samples A-F above.

EXAMPLE Undercoats are prepared by coating dispersions containing the following, on a polyethylene coated paper support at a gelatin coverage of 580 mg./ft. 4-phenylcatechol coverage of 30 mg./ft. and solvent coverage of 300 rng./ft.

(1) Di(tetrahydrofurfuryl) adipate (2) Tetrahydrofurfuryl pahnitate (3) Tetrahydrofurfuryl propionate (4) Tetrahydrofurfuryl benZoate (5) Bis(2-ethoxyethyl) adipate (6) Di propyl adipate (7) N,N,NNtetraethylphthalamide (8) Trioctyl phosphine oxide (9) N,N diethyldodecanamide (10) Tricresyl phosphate (11) Dibutyl phthalate The undercoats are overcoated with a silver chloride emulsion as in Layer II of Example I and then with a fogged emulsion prepared as in Example 1, Layer III and coated at 72 mg. silver/ft. and 215 mg. gelatin/ft? The resulting coatings are exposed by exposing to a 40 watt bulb at 27 inches through a parallel line test object covered with a step tablet, processed for 20 seconds at F. in an 8% potassium phosphate solution containing 0.1 g. KBr/liter and stopped for 20 seconds in a phosphoric acid bath. None had any efiect on press latitude except the first one, di(tetrahydrofurfuryl) adipate.

The invention has been described in detailwith particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as set forth in the appended claims.

We claim:

1. A photographic gelatin silver halide emulsion comprising a polyhydroxybenzene silver halide developing agent whose oxidation products render gelatin oleophilic and as a solvent for said developing agent, a di(tetrahydrofurfuryl) ester normally liquid at a temperature of about 25 C., said ester having not more than 20 carbon atoms, said silver halide emulsion uniformly hardened with a hardener such that the emulsion has a hardness equivalent to that of a gelatin emulsion hardened with about 2 grams to about 15 grams of dry formaldehyde per pound of gelatin.

2. An emulsion of claim 1 in which said developing agent is selected from the class consisting of halogen substituted, phenyl substituted and 2-6 carbon atom containing alkyl substituted polyhydroxybenzene developing agents.

3. An emulsion of claim 1 in which said developing agent is a phenyl substituted polyhydroxybenzene silver halide developing agent.

4. An emulsion of claim 1 in which said developing agent is a 2-6 carbon atom containing alkyl substituted polyhydroxybenzene silver halide developing agent.

5. An emulsion of claim 1 in which said developing agent is a 4-phenylcatechol silver halide developing agent.

6. An emulsion of claim 1 in which said ester is di(tetrahydrofurfuryl) adipate.

7. An emulsion of claim 1 in which said ester has the formula:

HzC-CH2 H2O oHomoRomoHo in which R is a dicarboxylic organic acid radical, said ester having no more than 20 carbon atoms.

8. An emulsion of claim 1 which is a direct positive emulsion.

9. An emulsion of claim 1 in which said solvent contains 075% by weight of another substantially water insoluble, low molecular Weight liquid ester having a boiling point above about C. and having a high solvent action for said silver halide developing agent.

10. An emulsion of claim 1 in which said solvent comprises a ratio of 1:1 to 1:15 developing agent to ester by weight.

11. A photographic element comprising a support having thereon said emulsion of claim 1.

12. A photographic element comprising a support having thereon a silver halide photographic emulsion layer and contiguous thereto a layer containing a substantially Water insoluble incorporated silver halide developing agent whose oxidation products render gelatin oleophilic dissolved in a liquid solvent comprising a di(tetrahydrofurfuryl) ester normally liquid at a temperature of about 25 C., said ester having not more than 20 carbon atoms,

the top layer of said element being a gelatin layer uniformly hardened with a hardener such that the said top layer has a hardness equivalent to that of a gelatin layer hardened with about 2 grams to about 15 grams of dry formaldehyde per pound of gelatin.

13. An element of claim 12 in which said developing agent is selected from the class consisting of halogen substituted, phenyl substituted and 2-6 carbon atom contain- 1 1 ing alkyl substituted polyhydroxybenzene developing agents.

14. A photographic element of claim 12 in which said di(tetrahydrofurfuryl) ester has the general formula:

H2O CH2 H2? CH H20 CHCHzOROH2CHC CH2 in which R is a dicarboxylic organic acid radical, said ester having no more than 20 carbon atoms.

15. A photographic element of claim 12 in which the said solvent contains 075% by weight of another substantially water insoluble, low molecular weight liquid ester having a boiling point above about 150 C. and having a high solvent action for the si ver halide developing agent.

16. A silver halide element of claim 12 in which said ester comprises a ratio of 1:1 to 1: 15 by weight developing agent to ester by weight.

17. A photographic element of claim 12 in which said solvent contains 25100% by weight of the said ester.

18. A photographic element of claim 13 in which said silver halide emulsion is a direct positive emulsion.

19. A photographic element of claim 12 in which said developing agent is selected from the class consisting of polyhydroxybenzene developing agents and substituted hydroxybenzene developing agents.

20. An element of claim 12 in which said developing agent is a phenyl substituted polyhydroxybenzene silver halide developing agent.

21. An element of claim 12 in which said developing agent is a 2-6 carbon atom containing alkyl substituted polyhydroxybenzene silver halide developing agent.

22. An element of claim 12 in which said developing agent is a 4-phenylcatechol silver halide developing agent.

23. An element of claim 12 in which said top layer comprises a fogged silver halide emulsion layer.

24. A photographic element comprising a support having thereon a silver halide photographic emulsion layer and contiguous thereto a layer containing a polyhydroxy benzene silver halide developing agent, said agent selected from the class consisting of halogen substituted, phenyl substituted and 2-6 carbon atoms containing alkyl substituted polyhydroxybenzene developing agents, the oxidation product of which renders gelatin oleophilic, the top layer of said element being uniformly hardened with a hardener such that the said top layer has a hardness equivalent to that of a gelatin layer hardened with about 2 grams to about 15 grams of dry formaldehyde per pound of gelatin, at least one of said layers containing a di(tetrahydrofurfuryl) ester normally liquid at a temperature of about 25 C., said ester having not more than 20 carbon atoms.

25. An element of claim 24 in which said top layer comprises a fogged silver halide emulsion layer.

26. A photographic gelatin silver halide emulsion of claim 1 in which said ester is an ester of adipic, glutaric, phthalic or succinic acid.

27. A photographic element of claim 12 in which said ester is an ester of adipic, glutaric, phthalic or succniic acid.

28. A photographic element of claim 24 in which said ester is an ester of adipic, glutaric, phthalic or succinic acid.

References Cited UNITED STATES PATENTS 2,234,615 3/1941 Alexander 260347.4 2,864,828 12/1958 Russell et a1. 260347.4 3,020,253 2/1962 Lukes 260-347.4 3,146,104 8/1964 Yackel et a1. 9666 NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant Examiner US. Cl. X.R. 

